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NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 3)

Take the NUMS Chemistry — Kinetics, Acids and Bases, Electrochemistry (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full…

What this test covers

30 NUMS Chemistry

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. In an experiment, doubling [A] doubles the rate while doubling [B] quadruples the rate. What is the rate law and overall order?
- A. Rate = k[A][B], second order
- B. Rate = k[A][B]², third order ✓
- C. Rate = k[A]²[B]², fourth order
- D. Rate = k[A]²[B], third order
Answer: B. Rate = k[A][B]², third order
Explanation: Rate ∝ [A]¹ (2¹ = 2) and ∝ [B]² (2² = 4); overall order = 1 + 2 = 3.
Q2. What are the units of the rate constant k for a second-order reaction when concentration is in mol dm⁻³ and time in seconds?
- A. mol² dm⁻⁶ s⁻¹
- B. dm³ mol⁻¹ s⁻¹ ✓
- C. mol dm⁻³ s⁻¹
- D. s⁻¹
Answer: B. dm³ mol⁻¹ s⁻¹
Explanation: k = rate/[conc]² = (mol dm⁻³ s⁻¹)/(mol² dm⁻⁶) = dm³ mol⁻¹ s⁻¹.
Q3. A first-order reaction has a rate constant of 0.0231 min⁻¹. What percentage of the reactant remains after 90 minutes? (ln 2 = 0.693)
- A. 25%
- B. 6.25%
- C. 50%
- D. 12.5% ✓
Answer: D. 12.5%
Explanation: t½ = 0.693/0.0231 = 30 min; 90 min is 3 half-lives, so (½)³ = 12.5% remains.
Q4. A first-order reaction has a half-life of 10 minutes. How long does it take for 80% of the reactant to be consumed?
- A. 20.0 min
- B. 16.0 min
- C. 30.0 min
- D. 23.2 min ✓
Answer: D. 23.2 min
Explanation: k = 0.693/10 = 0.0693 min⁻¹; t = (1/k)ln(1/0.20) = ln 5/0.0693 = 23.2 min.
Q5. A zero-order reaction has k = 0.020 mol dm⁻³ s⁻¹ and an initial concentration of 0.80 mol dm⁻³. What is its half-life?
- A. 10 s
- B. 35 s
- C. 40 s
- D. 20 s ✓
Answer: D. 20 s
Explanation: For zero-order t½ = [A]₀/2k = 0.80/(2 × 0.020) = 20 s.

The other 25 questions

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Q6. The rate of a reaction doubles for every 10 °C rise in temperature. By what factor does the rate increase when the temperature rises from 20 °C to 50 °C?
- A. 16
- B. 8
- C. 6
- D. 3
Q7. A reaction has an activation energy of 50 kJ mol⁻¹. By what factor does k increase when the temperature rises from 300 K to 310 K? (R = 8.314 J K⁻¹ mol⁻¹)
- A. 3.40
- B. 1.20
- C. 2.00
- D. 1.91
Q8. A catalyst increases the rate of a reversible reaction. Which quantity does it NOT change?
- A. The rate of the forward reaction
- B. The mechanism of the reaction
- C. The activation energy
- D. The equilibrium constant
Q9. Which statement about the molecularity of a reaction is correct?
- A. It can be found only by experiment from the rate law
- B. It is always equal to the overall order of the reaction
- C. It counts the species colliding in an elementary step and is a whole number
- D. It can be zero for zero-order reactions
Q10. Which of the following is NOT a requirement for a collision to produce a reaction according to collision theory?
- A. The molecules must collide
- B. The molecules must collide with proper orientation
- C. The molecules must have energy equal to or greater than the activation energy
- D. The colliding molecules must have identical masses
Q11. What is the pH of a 0.0005 M solution of Ba(OH)₂ at 25 °C, assuming complete dissociation?
- A. 10
- B. 10.7
- C. 3
- D. 11
Q12. What is the pH of a 0.10 M solution of acetic acid (Ka = 1.8 × 10⁻⁵)?
- A. 1.00
- B. 2.87
- C. 2.37
- D. 4.74
Q13. A 0.10 M weak monobasic acid has Ka = 1.0 × 10⁻⁵. What is its percentage ionisation?
- A. 10%
- B. 1.0%
- C. 0.01%
- D. 0.10%
Q14. 100 mL of 0.10 M HCl is mixed with 100 mL of 0.050 M NaOH. What is the pH of the mixture?
- A. 1.00
- B. 2.30
- C. 1.30
- D. 1.60
Q15. What is the pH of a buffer containing 0.10 M acetic acid and 0.20 M sodium acetate? (pKa = 4.76)
- A. 4.46
- B. 4.76
- C. 5.36
- D. 5.06
Q16. A solution of ammonium acetate (CH₃COONH₄) in water is approximately neutral. What is the reason?
- A. Neither ion undergoes hydrolysis in water
- B. Ka of NH₄⁺ and Kb of CH₃COO⁻ are nearly equal, so both hydrolyse equally
- C. The ions do not dissociate when dissolved in water
- D. It is a salt of a strong acid and a strong base
Q17. The pH of pure water at 100 °C is about 6.1. What does this indicate?
- A. The ionisation of water decreases at higher temperature
- B. Water becomes basic at 100 °C
- C. Water becomes acidic at 100 °C
- D. Water is still neutral because [H⁺] = [OH⁻], but Kw has increased
Q18. What is the conjugate base of the dihydrogen phosphate ion, H₂PO₄⁻?
- A. PO₄³⁻
- B. H₃O⁺
- C. HPO₄²⁻
- D. H₃PO₄
Q19. Which indicator is most suitable for the titration of acetic acid against NaOH?
- A. Methyl red
- B. Phenolphthalein
- C. Methyl orange
- D. Congo red
Q20. What is the oxidation number of carbon in methanol, CH₃OH?
- A. −4
- B. 0
- C. −2
- D. +2
Q21. In acidic solution, how many moles of Fe²⁺ are oxidised to Fe³⁺ by one mole of MnO₄⁻ (which is reduced to Mn²⁺)?
- A. 1
- B. 2
- C. 3
- D. 5
Q22. In a titration, 25.0 mL of an acidified Fe²⁺ solution requires 20.0 mL of 0.020 M KMnO₄. What is the molarity of the Fe²⁺ solution?
- A. 0.40 M
- B. 0.016 M
- C. 0.020 M
- D. 0.080 M
Q23. What is the standard EMF of a Zn–Cu galvanic cell? (E° Cu²⁺/Cu = +0.34 V, E° Zn²⁺/Zn = −0.76 V)
- A. +1.10 V
- B. +0.42 V
- C. +0.76 V
- D. −1.10 V
Q24. What is the EMF of the cell Zn | Zn²⁺ (0.010 M) || Cu²⁺ (1.0 M) | Cu at 25 °C? (E°cell = 1.10 V; use 0.0591 V)
- A. 1.10 V
- B. 1.22 V
- C. 1.04 V
- D. 1.16 V
Q25. Why does copper (E° = +0.34 V) not liberate hydrogen gas from dilute hydrochloric acid?
- A. Its E° is more positive than H⁺/H₂ (0.00 V), so it cannot reduce H⁺
- B. Copper is a non-metal and cannot lose electrons
- C. Copper forms an insoluble chloride layer that stops the reaction
- D. Hydrogen is more reactive than copper under all conditions
Q26. What mass of copper is deposited from CuSO₄ solution by a current of 2.0 A flowing for 965 s? (Cu = 63.5, F = 96 500 C mol⁻¹)
- A. 0.635 g
- B. 0.318 g
- C. 1.270 g
- D. 0.0100 g
Q27. What are the products at the cathode and anode during electrolysis of concentrated aqueous sodium chloride (brine) using inert electrodes?
- A. Na at the cathode and Cl₂ at the anode
- B. H₂ at the cathode and O₂ at the anode
- C. H₂ at the cathode and Cl₂ at the anode
- D. Na at the cathode and O₂ at the anode
Q28. For how long must a current of 3.0 A be passed through molten Al₂O₃ solution to deposit 2.7 g of aluminium? (Al = 27, F = 96 500 C mol⁻¹)
- A. 19300 s
- B. 3217 s
- C. 9650 s
- D. 28950 s
Q29. What happens to the sulphuric acid concentration in a lead–acid battery as it discharges?
- A. It stays constant throughout the discharge
- B. It decreases, because H₂SO₄ is consumed forming PbSO₄
- C. It increases, because water is consumed in the reaction
- D. It increases, because Pb²⁺ ions are released into solution
Q30. In the reaction BF₃ + F⁻ → BF₄⁻, what is the role of BF₃?
- A. Reducing agent, because it loses electrons
- B. Lewis acid, because it accepts an electron pair
- C. Brønsted acid, because it donates a proton
- D. Lewis base, because it donates an electron pair